The present invention relates to an electronic combination lock suitable for industrial, commercial or residential use and capable of operating independently of a central control system. More particularly, the present invention relates to an electronic combination lock with entry codes, lock-out codes and a programming access code (programming code) for entering a programming mode in which the entry codes and lock-out codes can be changed.
An electronic combination lock is desirable because the lock can be opened without a key. The problem of losing keys is eliminated, and the cost of producing keys is also eliminated. A basic electronic combination lock is disclosed in "Combination Lock," Hobby Electronics, vol. 3, no. 12, October 1981, pp. 21-23. To open the lock, a five digit combination is entered using numbered push buttons. If the buttons have been pressed in the correct order, and in fairly rapid succession, and if the entered code matches a predetermined code, the lock will open. However, this article does not disclose a way to change the code.
U.S. Pat. No. 4,532,507 (to Edson et al) discloses an electronic combination security system (such as an alarm) in which the codes for turning off the alarm can be changed. There is a keypad at which a temporary pass code or a permanent pass code can be entered to turn off the alarm. In addition, entry of the permanent pass code will allow the temporary pass codes to be changed by using function keys separate from the keypad. The function keys must be pressed within 45 seconds of entry of the permanent pass code. However, in the system of the Edson et al patent, the permanent pass code cannot be changed. Therefore, an unauthorized person who discovers the permanent pass code can always gain entry, no matter how often the temporary codes are changed. Moreover, if it is desired to prevent temporary codes from working for a period of time, e.g. during a temporary period of increased security, the codes must be deleted from the system and later re-entered into the system.